Lead generation relies heavily on effective landing pages to convert traffic into leads (conversions). If you don't have any landing pages, or at least any good ones, you won't be able to take advantage of your traffic.
The best way to find out what works on a landing page and what doesn't work is to run different variations to test them. But, it does help you get started on the right foot if you follow some standard guidelines when designing landing pages, then use data gathered to tweak and adjust them to increase conversions even more.
KISSmetrics put together a really nice and visually descriptive infographic The Blueprint for a Perfectly Testable Landing Page, which you can follow to create effective landing pages right from the beginning.
Make sure you're using some sort of a tracking service, like Google Analytics, to measure the traffic and conversions that come to your landing pages.
A good way to start is to create two identical landing pages, then change only 1 element on one of them. It can be anything you want to test. For example, an image, headline text, call to action button color, call to action text, even something as simple as text font. Whatever you change, make sure it is only one thing.
The reason for that is to make sure that whatever the results are you know exactly what caused it. This is called A/B split testing.
You can have more than two pages in you split test, keeping changes to one element. But the more pages you have, the more traffic you need to be certain of your results. There's no magic number, but the bigger the better.